1. Field of the Invention
The present invention relates to a container for containing a photosensitive material, such as photographic film or photographic printing paper, in light-tight fashion. In particular, the invention is a container for photosensitive material which has good light shielding characteristics and high strength. The present disclosure is based upon the disclosure of Japanese Appln. No. 4-141759 filed Jun. 2, 1992, which disclosure is incorporated herein by reference.
2. Description of the Related Art
Photographic film and photographic printing paper are contained in light-tight containers, because of the photosensitivity thereof. For example, in the known 135-size (35 mm) photographic film cassette, a photographic filmstrip wound on a spool is contained in a container made of a metal plate, and the container is used to house the film for photographing as well as for storage.
Recently, it is known to utilize a photographic film cassette in which a filmstrip, including a leader portion thereof, is entirely located within a cassette shell when the film cassette is not used. Such a cassette has a mechanism for advancing a leading end of the filmstrip to the outside of the cassette shell by rotating a spool of the cassette in an unwinding direction. This configuration makes the cassette easy to handle, because the leading end of the filmstrip does not extend outside the cassette shell when the cassette is loaded into and removed from a camera. For the same reason, this type of cassette is favorable for its light-shielding ability.
Specifically, U.S. Pat. No. 4,834,306 and Japanese Laid-open Patent Application No. 2-124564 each disclose a film cassette of the leader advancing type wherein a spool is provided with disks or flanges on both lateral sides of a film roll would on the spool. Circumferential or annular lips are formed on the periphery of the flanges to project in the axial direction of the spool so that the outermost convolution of the film roll is radially constrained by the lips. Ridges are formed on the lateral walls of the cassette shell for contact with the outside surface of the flanges, and press the flanges against the lateral sides of the film roll. Accordingly, the film roll is rotated together with the spool.
Spreader or guide projections are formed on the inside of the cassette shell at a position which is proximate a film passageway through which a leading end of the filmstrip is advanced to the outside of the cassette shell. The spreaders deflect the flanges outwardly to widen the spacings between the flanges, at positions thereof which are proximate the passageway, to prevent the outermost convolution of the film roll from contacting with the lips in the vicinity of the spreaders.
The cassette shell is provided with a separating claw disposed in a position corresponding to one of the spreaders. The separating claw is adapted to peel off the leading end of the filmstrip from the inner roll and guide it to the outside of the cassette shell through the film passageway when the leading end is freed form the radial confinement of the lips in the vicinity of the spreaders.
The spool, including the flanges, is made of resin. Also the cassette shell is composed of two shell halves produced by resin molding. The shell halves must be light-tight, and must be integrally formed with the spreaders, the separating claw and the ridges which are necessary for the above-described leader-advancing function.
In view of the foregoing, it is important to select an optimum composition of the resin material of the cassette shells in view of moldability as well as light shielding characteristics because light shielding is an essential function of cassette shells, and moldability greatly affects the efficiency of manufacturing of the cassette shells.
If cassette shells only require light shielding ability, they can be formed from any black resin material which is used to form the spools of the conventional film cassettes. However, the carbon content of conventional black resin material is so large that a product molded therefrom will be considerably weak when formed to a small thickness, as is required for cassette shells, (e.g., less than 1.0 mm). On the other hand, as the thickness of resin molded products increases, the cooling time generally increases in the molding process. A long cooling time not only extends the molding cycle, but also may often cause the products to incur sink marks.
Furthermore, because the photographic film of the film cassette is always used with the cassette shell, it is desirable to print information relating to the film on the cassette shell, and to make the appearance of the cassette shell attractive. Therefore, conventional cassette shells have information, marks or decorative patterns printed thereon. However, if the outer surface of the cassette shell is black it is difficult to clearly provide information or decorative patterns on the cassette shell without the use of an additional label, or the like.